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  • 1
    Electronic Resource
    Electronic Resource
    Semi-insulating GaAs: A possible substrate for a field-assisted positron moderator (1994)
    Springer
    Applied physics 59 (1994), S. 259-273 
    Details
    ISSN: 1432-0630
    Keywords: 78.70.Bj ; 79.90 ; 72.20.Ht
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Positron lifetime spectroscopy measurements have been carried out for semi-insulating GaAs with applied electric fields in the samples directed towards, and away from the positron injecting contact. The lifetime spectra have been decomposed into two components, the longer of which (≈400 ps) is characteristic of open volume defects at the metal-semiconductor interface through which positrons are injected. The interesting feature of these experiments is the large increase in the intensity of this interface component as the field is directed towards the contact. We show that this increase is caused by a significant fraction of implanted positrons drifting under the influence of a strong electric field produced by a layer of space-charge formed adjacent to the positron injecting contact. The general trend of the intensity variation is well explained by the proposed model. Experiments involving the application of an ac bias to the samples strengthen the suggestion that the space charge region is largely formed from ionized EL2 donors. The results of the present work indicate that semi-insulating GaAs possesses properties that make it a suitable material for the fabrication of a high efficiency (≈10%) room-temperature field-assisted positron moderator. The extraction of positrons from the GaAs substrate into the vacuum through a thin metalization is discussed based upon available positron affinities for the GaAs and various elemental metals. These data suggest that a few monolayers of a strongly electronegative metal such as Au or Pd may allow vacuum emission through quantum tunneling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348229
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Activities of enzymes involved in the metabolism of ether-linked lipids in normal and neoplastic tissues of rat
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism 619 (1980), S. 420-423 
    Details
    ISSN: 0005-2760
    Keywords: (Rat liver tumor) ; Acyl-CoA reductase ; Alkyl synthase ; Ether-linked lipid ; Fatty alcohol:-NAD^+ oxidoreductase
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0005-2760(80)90091-0
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    Paper (German National Licenses)
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  • 3
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    Quantification and characterization of volatiles evolved during extrusion of rice and soy flours (2000)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: NASA-Johnson Space Center is designing and building a habitat (Bioregenerative Planetary Life Support Systems Test Complex, BIO-Plex) intended for evaluating advanced life support systems developed for long-duration missions to the Moon or Mars where all consumables will be recycled and reused. A food system based on raw products obtained from higher plants (such as soybeans, rice, and wheat) may be a central feature of a biologically based Advanced Life Support System. To convert raw crops to edible ingredients or food items, multipurpose processing equipment such as an extruder is ideal. Volatile compounds evolved during the manufacturing of these food products may accumulate and reach toxic levels. Additionally, off-odors often dissipated in open-air environments without consequence may cause significant discomfort in the BIO-Plex. Rice and defatted soy flours were adjusted to 16% moisture, and triplicate samples were extruded using a tabletop single-screw extruder. The extrudate was collected in specially designed Tedlar bags from which air samples could be extracted. The samples were analyzed by GC-MS with special emphasis on compounds with Spacecraft Maximum Allowable Concentrations (SMACs). Results showed a combination of alcohols, aldehydes, ketones, and carbonyl compounds in the different flours. Each compound and its SMAC value, as well as its impact on the air revitalization system, was discussed.
    Keywords: Life Sciences (General)
    Type: Biotechnology progress (ISSN 8756-7938); Volume 16; 2; 299-301
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Correlation of lycopene measured by HPLC with the L, a, b color readings of a hydroponic tomato and the relationship of maturity with color and lycopene content (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: Tomatoes (Lycopersicon esculentum cv. Laura) were separated, according to the ripening stage, by a sensory panel into seven groups, and color was measured on the tomato surface with a Minolta Chroma meter. The L, a, b, hue, chroma, and lycopene content were plotted against the maturity stages of the tomatoes, and several good correlations were found. The a/b ratio and the lycopene content were the parameters that allowed six of seven maturity groups in the tomato to be statistically distinguished. The lycopene content, measured by HPLC, was also correlated with the color measurements, and the a, a/b, and (a/b)(2) color factors produced the best regressions. An estimation of the lycopene content in tomatoes can be achieved by using a portable chroma meter, with a possible field usage application. Equations to calculate the lycopene content of tomatoes based on the color readings are reported.
    Keywords: Life Sciences (General)
    Type: Journal of agricultural and food chemistry (ISSN 0021-8561); 48; 5; 1697-702
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Quality comparison of hydroponic tomatoes (Lycopersicon esculentum) ripened on and off vine (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: There is a general belief that the quality of tomatoes ripened on vine is better than tomatoes ripened off the vine, influencing among other parameters, the price of this commodity. We compared the quality of hydroponic tomatoes ripened on and off vine by chemical, physical, and sensory evaluation to find what attributes are affected and to what extent. Lycopene, beta-carotene, total and soluble solids, moisture content, ascorbic acid, acidity, pH, texture, and color were analyzed. Tomatoes ripened on vine had significantly more lycopene, beta-carotene, soluble and total solids, higher a* and lower L*, and were firmer. However, a 100-judge panel rated only the color and overall liking of the vine-ripened tomatoes as more intense than the fruit ripened off vine. Therefore, the chemical and physical differences were mostly not large enough to influence the panelist's perception. The characterization of tomatoes ripened on and off vine may help to guide post-harvest handling and treatment and to improve the quality of tomatoes ripened off vine.
    Keywords: Life Sciences (General)
    Type: Journal of food science (ISSN 0022-1147); 65; 3; 545-8
    Format: text
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    NASA TECHNICAL REPORTS
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